Method and means for reducing radio interference



Feb. 7, 1933. E. N, HYDE 1,896,819

METHOD AND MEANS FOR REDUCING RADIO INTERFERENCE Filed May 5, 1931Patented Feb. 7, 1933 PATENT OFFICE ERNEST N. HYDE, OF PHILADELPHIA,PENNSYLVANIA METHOD AND MEANS FOR REDUCING RADIO INTERFERENCEApplication filed May 5,

This invention relates to a method and means for reducing to the extentof practical elimination radio interference caused by the making andbreaking of an electric circuit,

which making or breaking may be complete or only partial, as in the caseof thermally operated flashers for signs or the like.

In cases where circuits carrying currents for power purposes are openedor closed,

either partially or completely, there are propagated disturbances ofhigh frequency which produce audible cracks or noises, depending uponthe frequency of such breaks, in radio receivers. Such making orbreaking is particularly annoying when it occurs in connection with theoperation of a motor provided with a commutator since in such cases thedisturbances follow each other in rapid succession producing acontinuous noise.

It is the object of the present invention to provide both a method andmeans for carrying out the method which are both of general applicationfor the elimination of interference of the type mentioned above,occurring because of the use of motors, sign flashers,

switches, or the like.

Detailed objects of the invention relating particularly to preferredconstructions will be apparent from the following description read inconjunction with the accompanying drawing in which:

Fig. 1 is a wiring diagram showing one preferred form of the invention;and

Fig. 2 is a wiring diagram showing a modii fication.

Referring first to the modification illustrated in Fig. 1, 2 and 4represent currentcarrying wires which may lead from an alternating ordirect current source to a load.

It will be understood that these wires may be considered to be parts ofthe wiring of a motor. Located in series with one of these wires is asuitable capacity indicated as a condenser 6. While in the preferredembodiment the capacity consists of a separate condenser, it may undercertain circumstances be provided by the distributed capacity of thecoil 8 which, in Fig. 1, is shown as shunted across the condenser 6 inseries with the contacts 10. The contacts are also merely dia- 1931.Serial No. 535,119.

grammatically illustrated and may be of any i K of the usual circuitmaking or breaking forms. For example, they may be switch contacts orthe contacts of a thermal flasher, in which case a circuit is notcompletely open because the contacts remain shunted by the highresistance heater wire. Or the contacts here diagrammaticallyillustrated may consist of the circuit interrupting arrangement providedby the brushes and commutator of a direct or alternating current motor.

In any case, the essence of the invention comprises the location of thecontacts, this word being used in a broad sense, within theelectromagnetic field of coil 8, the contacts being preferably locatedat the point of maximum intensity of this electromagnetic field which,in the case of a solenoid, would be its geometrical center.

As a specific instance of one device which is found to be very effectivein producing substantially an entire elimination of interference, theremay be cited a case in which a lamp load was supplied, being providedwith the arrangement of Fig. 1, the condenser 6 having a capacity ofapproximately .400 mfd. and the coil 8 comprising 72 turns of #22 copperwire wound as a solenoid having a diameter of about 4.5 inches. In thiscase the breaker consisted of a mercury switch, the load beingapproximately 260 watts. It is found, however, that very largevariations may be made in the constants of the circuit. For example, thecondenser may be from .0006 mfd. up to .500 mfd., or even largerLikewise, the inductance of the coil may vary widely as will be broughtout more particu larly in connection with the second modification.

In the modification illustrated in Fig. 2 there is again provided acondenser 6 in series with the line while shunted across this condenserare the coil 12 and contacts 16 in series with each other. In this casethe coil 12 consists of iron wire wound upon a wooden support 14, thecontacts 16 being located in the geometrical center of the form. In thiscase. of course the electromagnetic field at the contacts issubstantially equivalent to that produced by a single turn. However, theinductance of the coil is quite large, particularly because of themagnetic material of which the coil is made. As an alternativearrangement a magnetic core may be used upon which copper wire could bewound or parallel to which the wire convolutions may lie, Whereby againa relatively high inductance would result. Comparing the arrangement inFig. 2 with that in Fig. 1, both of which are found to be satisfactory,it will be seen that the inductance as well as the capacity may varywithin wide limits, the inductance in Fig. 2,

being considerably larger than that in Fig. 1. If the core of thearrangement of Fig. 2 is metallic it may form part of the circuit, thatis, the contacts, core and coil may all be in series shunted across thecondenser.

Both the coil and condenser may, of course,

. take various forms depending'upon conditions, and, in the case of thecoil, the required current carrying capacity, since the coil preferablycarries the full load. Alternatively, of course, the coil may, in thecase of large loads, be shunted by a lower resistance path so that itcarries only a fraction of the total the contacts being locatedsubstantially at the position of maximum intensity of theelectromagne'tic field of the coil, and a capacity shunting the coil andcontacts, the coil and capacity forming a circuit having a high naturalfrequency.

In testimony of which invention, I have hereunto 'set my hand, atPhiladelphia, Pennsylvania, on this 1st day of May, 1931.

ERNEST N. HYDE.

current. Of course, in certain arrangements several coils arranged inseries or parallel may be used, the contacts being located in theircombined fields or in the fields of any one of them. 7 V 7 It is'foundthat interferencemay be substantially eliminated even though thecontacts may not be in series with the coil in whose field they lieproviding that this coil is supplied with the same type of current asthat interrupted by the contacts and both are.

in synchronism with each other. For example, if 60 cycle alternatingcurrent is being interrupted then it is found thatthe contacts in suchcircuit may be located in the field of a coil shunted by a condensercarrying 60 cycle current even though the current thereto may not beinterrupted by the movement of the contacts.

Still more 'efiectiveness may be given to the device in certaininstances by shielding the coil and contact points by their locationwithin a conductive container and this shielding container .may begrounded. In certain cases where the current density is very high, thewhole device may be immersed in oil or other liquids to suppress arcing,or they may be enclosed in sealed or unsealed glass or quartz ormetalcontainers or shields.

What I claim and desire to protect by Letters Patent is i i 1. Anarrangement for reducing electromagnetic radiations due to the openingorclosing of contacts in a circuit, including a coil arranged tocarrycurrent, the contacts being located in the field of the coil, and acapacity in parallel with the coil, the coil and capacity forming acircuit having a high natural frequency.

